Genetic methods to control protein levels are extremely valuable tools for probing the basic biology of any organism. Two commonly employed tools are RNA interference and conditional expression, neither of which has been successfully implemented in malaria research. We are developing a new method to control proteins in the secretory pathway of malaria parasites. Over 20% of the proteins encoded by the Plasmodium falciparum genome are thought to pass through the secretory system on their way to organellar or extracellular destinations. These proteins have key roles in parasite metabolism, nutrient acquisition, invasion, host cell remodeling, and other critical aspects of parasite biolog. The goal of this project is to design and optimize a conditional probe to control the localization f soluble secretory proteins in P. falciparum. This method will then be validated by applying it to two biological targets: one in the apicoplast organelle and one which resides in the parasitophorous vacuole. Successful development of a conditional localization tool will enhance our ability to probe the basic biology of malaria parasites and will allow us to validate potential targets for therapeutic intervention.